36 : Computational mechanics for engineers

Incontournable, la mécanique numérique s’insère aujourd’hui dans l’ensemble de la chaîne de conception rapide des produits fabriqués par l’industrie. S’appuyant sur les outils de modélisation géométrique et de visualisation, et intégrant les outils de simulation et d’optimisation, elle réduit les délais de conception, limite les erreurs et s’insère dans l’esprit du développement durable en aidant à concevoir des produits de plus en plus respectueux de l’environnement.

36 : Computational mechanics for engineers

Computational hydraulics at UTC

Computational modelling is not limited to industrial artefacts. The research tea in computational hydraulics housed by UTC applied this approach to flood situations or coastal water submersion, and also to many other subjects that have a connection with water, waterways and navigation ...

For the analysis of floods and coastal submersion, public authorities now use computational modelling to draft policy and regulations in this area. The computational hydraulics laboratory (LHN) created in 2003, housed by the UTC Roberval Laboratory is the work place for 3 research scientists of the French Ministry for Ecology specialists of these issues.

The group has been working together since 1991 and focuses on the question of risks related to water notably faced with the needs expressed by the Risk Prevention Directorate General. The group also investigates river and sea transportation, energy recuperation from currents and waves and looks at the consequences of impending climatic change, in terms to rising sea levels.

Specific tools

Ever since the end of the 1970s when computational tools specific to water problems were being developed and introduced at the CEREMA Directorates for Waterways, Rivers and Maritime Transport, Philippe Sergent, the current Senior Scientific Officer has been working on these questions with his LHN partners. The REFLUX computational protocol - that dates back to the 1980s - integrates a first level of data organization, a computational module and a tool to display the results.

"REFLUX was used up till year 2000 and was then gradually replaced by the EDF protocol "TELEMAC" details Philippe Sergent. What is special about these studies is the sheer volume of geographic data that requires tools with a capacity to store and process them. Displaying the results is also difficult, inasmuch as the area involved is measured in thousands of km². "Under these conditions, the calculations are very long compared with what we traditionally see in the mechanical engineering sector," underlines Philippe Sergent. Another specific feature of the questions is the large number of unknowns compared with classic modelling in industry.

To illustrate, it is impossible to take the seasonal factor into account (effects on vegetation) when an area is being modelled for flood risks. Existence of hedges in built-up areas and the capacity of the soils to absorb excess surface water are also difficult factors to handle.

Optimizing ship movements

Another novelty here is to work with 3D structures to model ship movements. The models serve to better understand the resistance to progression of a ship in a confined volume, for the purpose of optimizing fuel consumption. The shallower the water under the ship's hull, or the narrower the navigation channel, the higher are both water resistance and fuel consumption.

By varying the vessel speed, gains of between 5 and 10% can be expected. And these figures too can be improved further if the lock management is optimized. "For hydrodynamic models, calculations can take up to one month" details Philippe Sergent. Pluridisciplinary approaches Other specific developments relate to cost/benefits analyses used to optimize the approaches needed to face potential situations of flooding and/or submersion.

These studies require pluridisciplinary skills in order for the economic, environmental and societal aspects to be taken into account properly. The major challenges today are tied to new hydro-power generation schemes, and also to climate studies. In a general sense, the 'blue power' growth implies that all activities that appertain to the seas and oceans (energy, mineral resources, offshore ports, etc.) offer considerable prospects for future LHN research.

Another strong challenge relates to possible sea level rising over the coming 50 or 100 years. With this project in mind, public authorities will need new tools to help them redefine the next strategy to follow if we want to minimize the impacts of climate change.